Polyurethane foam is obtained by the reaction of a polyol compound with an isocyanate compound which gives rise to a macromolecular compound. The reaction of water with the isocyanate compound which generates carbon dioxide gas and the gasification of a foaming agent which produce a foam proceed at the same time. For the purpose of producing a foam with desired physical properties, it is necessary that the balance between the production of the macromolecular compound and the phenomenon of foaming be controlled and the cellular structure of the foam in the process of growth be controlled.
Generally, a polysiloxane compound, particularly a polysiloxane-polyoxyalkylene copolymer, is used as the foam uniformizing agent. A foam stabilizer of a varying structure is used to suit the percentage composition of raw material components and the physical properties of the desired foam. When highly elastic soft and semi-rigid polyurethane foams a are made using conventional polyurethane foam uniformizing agents, these foams shrink because these agents excessively stabilize bubbles to the extent of impeding the conversion of such bubbles into open cells. Generally, for ensuring safe production of these foams, the foam stabilizer to be used possesses weak foam uniformizing power and added defoaming agent is often required for the purpose of controlling the formation of open cells. Examples of typical defoaming agents are low-molecular organic silicone compounds such as diorganopolysiloxanes, diorganopolysiloxane-polyoxyalkylene copolymers, and diorganopolysiloxanes having organic functional groups added thereto in the place of polyoxyalkylene chains.
When such low-molecular organic silicone compounds are used as defoaming agents in the production of a highly elastic soft and semi-rigid polyurethane foam, the process ranges of the reaction conditions and the amounts of foam stabilizer and catalyst to be used during the production of the foam are so restricted as to make it difficult to produce foams of good quality. Further, when these foams are produced in a complicated shape, the they suffer the disadvantage of impaired flowability of the reaction mixture resulting in the generation of voids.